If you’re wondering where Alzheimer’s research might be headed after the latest large-scale failure of a clinical trial based on the “amyloid hypothesis,” check this out.
Plaques. Tangles. Clumps. These are all pathological signs of neurodegenerative diseases that scientists can see under the microscope. But they don’t explain most of the broader trends of cognitive resilience or decline in aging individuals. What’s missing?
A recent proteomics analysis in Nature Communications from Emory researchers identifies key proteins connected with cognitive trajectory – meaning the rate at which someone starts to decline and develop mild cognitive impairment or dementia.
This paper fits in with the multi-year push for “unbiased” Alzheimer’s/aging research at Emory. The lead and senior authors are Aliza and Thomas Wingo, with proteomics from biochemist Nick Seyfried and company.
The proteins the Emory team spotlights are not the usual suspects that scientists have been grinding on for years in the Alzheimer’s field, such as beta-amyloid and tau. They’re proteins connected with cellular energy factories (mitochondria) or with synapses, the connections between brain cells.
“Our most notable finding is that proteins involving mitochondrial activities or synaptic functions had increased abundance among individuals with cognitive stability regardless of the burden of β-amyloid plaques or neurofibrillary tangles,” the authors write. “Taken together, our findings and others highlight that mitochondrial activities would be a fruitful research target for early prevention of cognitive decline and enhancement of cognitive stability.” Read more
Neuroscientist and geneticist David Weinshenker makes a case that the locus coeruleus (LC), a small region of the brainstem and part of the pons, is among the earliest regions to show signs of degeneration in both Alzheimer’s and Parkinson’s disease. You can check it out in Trends in Neurosciences.
The LC is the main source of the neurotransmitter norepinephrine in the brain, and gets its name (Latin for “blue spot”) from the pigment neuromelanin, which is formed as a byproduct of the synthesis of norepinephrine and its related neurotransmitter dopamine. The LC has connections all over the brain, and is thought to be involved in arousal and attention, stress responses, learning and memory, and the sleep-wake cycle.
Cells in the locus coeruleus are lost in mild cognitive impairment and Alzheimer’s. From Kelly et al Acta Neuropath. Comm. (2017) via Creative Commons
The protein tau is one of the toxic proteins tied to Alzheimer’s, and it forms intracellular tangles. Pathologists have observed that precursors to tau tangles can be found in the LC in apparently healthy people before anywhere else in the brain, sometimes during the first few decades of life, Weinshenker writes. A similar bad actor in Parkinson’s, alpha-synuclein, can also be detected in the LC before other parts of the brain that are well known for damage in Parkinson’s, such as the dopamine neurons in the substantia nigra.
“The LC is the earliest site to show tau pathology in AD and one of the earliest (but not the earliest) site to show alpha-synuclein pathology in PD,” Weinshenker tells Lab Land. “The degeneration of the cells in both these diseases is more gradual. It probably starts in the terminals/fibers and eventually the cell bodies die.” Read more
Posted on July 3, 2018
In recent news stories about Alzheimer’s disease research, we noticed a word popping up: unbiased. Allan Levey, chair of Emory’s neurology department and head of Emory’s Alzheimer’s Disease Research Center, likes to use that word too. It’s key to a “back to the drawing board” shift taking place in the Alzheimer’s field.
Last week’s announcement of a link between herpes viruses and Alzheimer’s, which Emory researchers contributed to, was part of this shift. Keep in mind: the idea that viral infection contributes to Alzheimer’s has been around a long time, and the Neuron paper doesn’t nail down causality.
Still, here’s an example quote from National Institute on Aging director Richard Hodes: “This is the first study to provide strong evidence based on unbiased approaches and large data sets that lends support to this line of inquiry.”
What is the bias that needs to be wrung out of the science? The “amyloid hypothesis” has dominated drug development for the last several years. Amyloid is a main constituent of the plaques that appear in the brains of people with Alzheimer’s, so treatments that counteract amyloid’s accumulation should help, right? Unfortunately, antibodies against amyloid or inhibitors of enzymes that process it generally haven’t worked out in big clinical trials, although the possibility remains that they weren’t introduced early enough to have a decent effect. Read more
Removal of a regulatory gene called LSD1 in adult mice induces changes in gene activity that look unexpectedly like Alzheimer’s disease, scientists have discovered.
Researchers also discovered that LSD1 protein is perturbed in brain samples from humans with Alzheimer’s disease and frontotemporal dementia (FTD). Based on their findings in human patients and mice, the research team is proposing LSD1 as a central player in these neurodegenerative diseases and a drug target.
David Katz, PhD
The results were published Oct. 9 in Nature Communications.
In the brain, LSD1 (lysine specific histone demethylase 1) maintains silence among genes that are supposed to be turned off. When the researchers engineered mice that have the LSD1 gene snipped out in adulthood, the mice became cognitively impaired and paralyzed. Plenty of neurons were dying in the brains of LSD1-deleted mice, although other organs seemed fine. However, they lacked aggregated proteins in their brains, like those thought to drive Alzheimer’s disease and FTD.
“In these mice, we are skipping the aggregated proteins, which are usually thought of as the triggers of dementia, and going straight to the downstream effects,” says David Katz, PhD, assistant professor of cell biology at Emory University School of Medicine. Read more